<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .clearfix:before,
        .clearfix:after {
            content: "";
            display: table;
        }

        .clearfix:after {
            clear: both;
        }

        .clearfix {
            *zoom: 1;
            /*IE/7/6*/
        }

        .div {
            width: 200px;
            height: 100px;
            border: 2px solid #ff0;
            position: relative;
        }

        .div::before {
            content: '';
            width: 0;
            height: 0;
            border: 20px solid;
            position: absolute;
            bottom: -40px;
            left: 140px;
            border-color: #ff0 transparent transparent;
        }

        .div::after {
            content: '';
            width: 0;
            height: 0;
            border: 20px solid;
            position: absolute;
            bottom: -36px;
            left: 140px;
            border-color: #fff transparent transparent;
        }

        .div1 {
            width: 50px;
            height: 50px;
            border: 50px solid;
            border-color: yellow skyblue pink deeppink;
        }

        .tag {
            width: 126px;
            height: 30px;
            border: 2px solid red;
            position: relative;
        }


        .tag::before {
            content: '';
            width: 0;
            height: 0;
            border: 3px solid;
            border-color: red transparent transparent;
            position: absolute;
            left: 30px;
            bottom: -8px;
        }

        .tag::after {
            content: '';
            width: 0;
            height: 0;
            border: 3px solid;
            border-color: #fff transparent transparent;
            position: absolute;
            left: 30px;
            bottom: -6px;
        }
    </style>
</head>

<body>
    <div>
        <div class="div"></div>

        <p>1.下面是一个div.长宽为50*50的正方形，边框宽度为50</p>
        <div class="div1"></div>
    </div>
    <div class="tag"></div>
</body>

</html>